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HyperPhysics: Global Positioning Satellites

The image shows a Global Positioning System (GPS) receiver that pinpoints a cyclist's location to an accuracy of about 10 m. The receiver analyzes radio signals from several GPS satellites, each containing an atomic clock accurate to about one second every 30,000 years. For more on GPS, see HyperPhysics: Global Positioning Satellites and also this NASA site.

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Geocaching

Do you have a GPS at home? Try taking it outside and exploring your area with Geocaching. It's a modern-day treasure hunting game, using your GPS to find packages left by fellow "Geocachers." All you have to do is sign up on the website, search for geocaches near you, put in the coordinates, and go! Be sure to have an adult with you.

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How does GPS work?

The photo shows a Global Positioning System satellite. To find out how the system works, visit How does GPS work?. Be sure to see the video to understand how three or four different GPS satellites specify your position on Earth.

Einstein's Relativity and Everyday Life

If you rely on a GPS to navigate, then you need Einstein's theories of relativity--special relativity because the GPS satellites are moving fast relative to you, and general relativity because the GPS satellites are in a different gravitational field than you are. Without correction for relativistic effects, errors in GPS positions would increase by 10 km for every day the system operates! To learn more visit Einstein's Relativity and Everyday Life, and also this Ohio State astronomy page.